Survivability has been defined as “the capability of a network to maintain service continuity in the presence of faults.” D. Awduche, A. Chiu, A. Elwalid, 1. Widjaja, and X. Xiao, “Overview and Principals of Internet Traffic Engineering,” Re-quest for Comments (Informational) RFC 3272, Internet Engineering Task Force, May 2002. Since the Internet has become a key for communications and commerce in the world today, network survivability has assumed great importance. Networks need to be designed so that connectivity is maintained in the face of failures in the network. Links have to be provisioned so that there is sufficient capacity to carry the additional network traffic coming their way in the event of failures. Protecting the service quality (minimally assuring availability of capacity) in the face of network failures requires redundant resources (over what is required for failure free operation) which increases the cost of network operation.
Accordingly, there is a need for methods to evaluate the extra cost of survivability and to reduce the cost of network operation with survivability.